1. Field of the Invention
This invention relates to a novel ethylene/alpha-olefin copolymer. More specifically, it relates to an ethylene/alpha-olefin copolymer having a low molecular weight and a relatively narrow molecular weight distribution, a process for its production, and its use as a synthetic lubricant oil, a fuel oil additive and a lubricant oil additive.
2. Description of the Prior Art
It is known that an ethylene/alpha-olefin copolymer having a low molecular weight which is useful as a synthetic lube oil is obtained by copolymerizing ethylene with an alpha-olefin having at least 3 carbon atoms in the liquid phase in the presence of a catalyst composed of a combination of a soluble vanadium compound and an organoaluminum compound in the co-presence of hydrogen (see U.S. Pat. No. 3,851,011). When the copolymer is produced by the method specifically disclosed in the Example of this U.S. Patent, it has poor uniformity (namely, it has broad molecular weight and composition distributions and sometimes it is obtained as a milky liquid or a white paste). When the product obtained has a low viscosity, it does not have a high flash point as a lubricant oil unless a low-molecular-weight portion is removed. On the other hand, if a product having a high viscosity is obtained, it has an excessively high pour point and is not practical as a lube oil. Oils which have a viscosity at 100.degree. C. of at least 60 centistokes are useful as lube oils for high loads. Those copolymers which are disclosed in the above Patent and have a viscosity in this range have too high a pour point to be used for practical applications. The U.S. Patent suggests that the copolymer can be fractionally distilled, and that a product having a narrow boiling point range obtained by fractional distillation can remove the aforesaid defects with regard to pour points and flash points. It is extremely difficult in this case, however, to obtain a product having a satisfactorily high viscosity index.
Japanese Patent Publication Nos. 37237/1975 and 7717/1976 suggest processes for producing an ethylene/alpha-olefin copolymer having a low molecular weight, and state that the production of copolymers having a narrow molecular weight distribution is possible. These processes, however, have the defect that special compounds must be used as a molecular weight controlling agent or a catalyst promotor. In addition, copolymers having a sufficiently low molecular weight, such as those of lubricant oil grade, which are prepared in accordance with the specific disclosures of these Patent Publications do not have a sufficiently narrow distribution of molecular weight, and, therefore, have the same defects as described above with regard to U.S. Pat. No. 3,851,011.
It is an object of this invention therefore to provide an ethylene/alpha-olefin copolymer having a narrow molecular weight distribution.
Another object of this invention is to provide a process for producing the aforesaid copolymer in a continuous manner.
Still another object of this invention is to provide a synthetic lubricant oil having a low evaporation loss, a high flash point, excellent low-temperature flowability, good shear stability, good oiliness, and a high viscosity index.
Yet another object of this invention is to provide a fuel oil having excellent low-temperature flowability.
Other objects and advantages of this invention will become apparent from the following detailed description.